The present invention relates to a method for fabricating an electrode of a field-effect-controllable semiconductor component and to a field-effect-controllable semiconductor component.
In the course of an increasing integration density in integrated circuits, endeavors are made to integrate power transistors, in particular power field-effect transistors, and their associated drive circuit or drive logic in a semiconductor body.
Power transistors are usually transistors of vertical design, i.e. source and drain terminals of the transistors are situated on opposite sides of the semiconductor body, in which case the gate electrode can be arranged in a trench in a manner insulated from the semiconductor body. In components of this type, a conductive channel runs through the semiconductor body in the vertical direction. By contrast, components, in particular transistors, of the drive circuit are usually designed as lateral components, i.e. the terminals of these transistors are situated at one side of the semiconductor body and a conductive channel in the case of these transistors usually forms in the lateral direction in the semiconductor body. The different geometrical construction of the power transistors and of the transistors of the drive logic means that different method steps are required to fabricate them.
This does not constitute a problem if the power transistors and the drive logic are realized in different semiconductor bodies. However, if the power transistors and the components of the drive logic are intended to be integrated in a single semiconductor body, there is a need to be able to jointly utilize as many method steps as possible for the power transistor part and the drive logic part. Problems are posed here in particular by the fabrication of electrodes of the power transistors and of the transistors of the drive logic.
In the case of transistors of lateral design, the control electrodes, i.e. the gate electrodes in field-effect transistors, are fabricated by depositing an electrode layer onto an insulation layer on the semiconductor body. In the case of vertical power transistors designed as so-called trench transistors, in which the control electrode is thus formed in a trench of the semiconductor body, the trench is filled with an electrode material after the fabrication of an insulation layer at the trench surface, for this purpose an electrode material usually being deposited onto the semiconductor body, and hence also into the trenches. The thickness of the electrode material that is to be deposited in this case is dependent on the width of the trench which is to be filled. Thus, the thickness of the deposited electrode material must approximately correspond to the trench width in order to fill the trench by deposition of the electrode material and to obtain an approximately planar surface after etching-back of the electrode layer on the surface of the semiconductor body. In the case of trenches having a width of 800 nm, it is customary at the present time to deposit an electrode layer having a thickness of approximately 1 xcexcm. However, an electrode layer this thick is not suitable for fabricating gate electrodes of the drive logic, for which a thinner electrode layer has to be provided.
It is an aim of the present invention, therefore, to provide a method for fabricating an electrode of a field-effect-controllable semiconductor component which can equally be used for fabricating an electrode of a power transistor and for fabricating an electrode of a transistor of a drive logic.
This aim is achieved by a method for fabricating an electrode of a field-effect-controllable semiconductor component, the method having the steps of providing a semiconductor body having a first zone of a first conduction type and, disposed above the latter, a second zone of a second conduction type, and at least one trench that extends into the semiconductor body in the vertical direction through the second zone, fabricating a first insulation layer at least in the region of the second zone in the at least one trench, applying a first layer made of electrode material to the semiconductor body, applying an intermediate layer to the first layer made of electrode material, applying a second layer made of electrode material to the intermediate layer, removing the second layer made of electrode material and of the intermediate layer, the intermediate layer and the second layer made of electrode material at least partly remaining in the at least one trench, and patterning the first layer made of electrode material.
The subclaims relate to advantageous refinements of the method according to the invention.
In the method according to the invention, firstly provision is made of a semiconductor body having a first zone of a first conduction type and, arranged above the latter, a second zone of a second conduction type, and at least one trench which extends into the semiconductor body in the vertical direction through the second zone. The fabrication of such a semiconductor body with the features mentioned is adequately known from methods for fabricating power transistors. Afterward, a first insulation layer is fabricated at least in the region of the second zone in the at least one trench. This insulation layer may be, in particular, a layer made of an oxide of the semiconductor material which is produced by means of a thermal method. Afterward, a layer made of electrode material is deposited onto the semiconductor body and hence also in the at least one trench. In a next method step, an intermediate layer is applied to said first layer made of electrode material, on which intermediate layer a second layer made of electrode material is then applied. The second layer made of electrode material and the intermediate layer are then removed above the semiconductor body, the intermediate layer and the second layer made of electrode material at least partly remaining in the trench. Afterward, the first layer made of electrode material is patterned in order to form the electrode.
The present method, in which an electrode of a field-effect-controllable semiconductor component is fabricated by deposition of a first electrode layer, an intermediate layer and a second electrode layer, is suitable both for fabricating a control electrode of a power transistor in a trench of the semiconductor body and for fabricating a control electrodexe2x80x94arranged on a surface of the semiconductor bodyxe2x80x94of a transistor of lateral design. In this case, the thickness of the first electrode layer is chosen in such a way that it is suitable for forming a control electrode, or gate electrode, of a lateral transistor of the drive logic. In this case, this electrode layer is usually so thin that the trenches of the later power transistor are not completely filled. In the method according to the invention, the trenches are filled by means of the second electrode layer which is deposited onto the intermediate layer and whose thickness is chosen in such a way that the trenches are completely filled. After the removal of the second electrode layer and the intermediate layer from regions above the semiconductor body, only the first thinner electrode layer remains on the semiconductor body for the as purpose of forming control electrodes of the drive logic, while the trenches are completely filled by the first thinner electrode layer and the second electrode layer applied above the latter. In the method according to the invention, the intermediate layer serves in particular as a stop layer during an etching operation in which the second electrode layer is removed from the surface of the semiconductor body. The intermediate layer is subsequently removed in a further method step.
In accordance with one embodiment of the invention, it is provided that before the fabrication of the first insulation layer in the at least one trench, a second insulation layer is fabricated which at least partly covers the surface of the at least one trench. This second insulation layer is thicker than the first insulation layer and covers the surface of the at least one trench preferably below the second zone. The thickness of this second insulation layer is preferably chosen in such a way that, after the fabrication of the first insulation layer in the trench in the region of the second zones and the deposition of the first layer made of electrode material, the trench is completely filled with electrode material where the second insulation layer is applied.
As already mentioned, in vertical power transistors, a conductive channel runs in the vertical direction in the semiconductor body. In transistors it is known to arrange so-called field plates along the conductive channel, the use of which field plates makes it possible to achieve a lower resistance of the transistor in the on state with a breakdown voltage that remains the same or is increased. In this case, that section of the first electrode layer which is arranged on the second insulation layer in the region of the first zone of the semiconductor body in the trench acts as such a field plate.
In accordance with a further embodiment of the invention, it is provided that the semiconductor body has at least two trenches, in which case, before the method step for fabricating the first electrode layer in one of the trenches, a second insulation layer is fabricated which covers the surface of the trench in the region of the first zone and second zone of the semiconductor body. In this case, the thickness of this second insulation layer is chosen in such a way that, after the deposition of the first layer made of electrode material, said trench is completely filled with electrode material. It is known to realize power transistors from a plurality of identically constructed cells which are interconnected. The trench which is completely filled with the second insulation layer and the first layer made of electrode material in this case serves for laterally delimiting the cell array, the section of the first layer made of electrode material in this trench acting as a field plate. This field plate is usually connected to the same potential as the control electrodes in the rest of the trenches, the second insulation layer being too thick to allow the field plate to act as a gate electrode.
The present invention furthermore relates to a field-effect-controllable semiconductor component having a semiconductor body with a first zone of a first conduction type, a second zone of a second conduction type, and at least one trench extending into the semiconductor body in the vertical direction of the semiconductor body through the second zone, a control electrode formed in the trench, an insulation layer formed in the trench and insulating the control electrode from the semiconductor body. The control electrode has a first electrode section adjacent to the insulation layer, a second electrode section, and an intermediate layer formed between the first and second electrode sections.